Venting device for a fuel tank of an internal combustion engine

ABSTRACT

A venting device for a fuel tank of an internal combustion engine having activated carbon filters via which the fuel tank is vented. During the shut-off phase of the internal combustion engine, the activated carbon filters absorbs the fuel which evaporates in the tank. In the operating phase of the internal combustion engine, the activated carbon filters are regenerated by flushing air. To keep down the flushing air required for regeneration, the activated carbon filter is subdivided into two filter parts, the volume of the first filter part being dimensioned so that, in the shut-off phases of the internal combustion engine, the first filter part reaches a high level of loading. Due to a diffusion-hindering connection between the two filter parts, the second filter part only likewise absorbs fuel vapor after the degree of saturation of the first filter part has been reached.

PRIOR ART

The invention starts from a venting device for a fuel tank of aninternal combustion engine as set forth hereinafter.

Such a venting devices (sic) serves to prevent fuel which evaporates inthe fuel tank, so-called fuel vapour, which arises, in particular,during the filling of the fuel tank or in the hot shut-off phase of theinternal combustion engine, from escaping into the atmosphere, insteadbeing stored in a fuel vapour filter. During the operation of theinternal combustion engine, the filter is then regenerated by flushingwith fresh air which is sucked in by the intake system of the internalcombustion engine via the fuel filter. The fuel-laden flushing air isthen fed to the internal combustion engine in metered fashion forcombustion (DE 33 46 103 C2, DE 38 02 664 C1).

In the U.S.A., such venting devices must be subjected to a so-called"on-board-refuelling test" to prove their efficiency, in which test afixed limiting value for the hydrocarbons set free with the evaporationof fuel must be complied with. In such a test, a number of operatingcycles of the internal combustion engine with intermediate shut-offphases are performed, starting from a fully laden fuel vapour filter.After the last shut-off phase, the fuel tank is filled. The hydrocarbonvalues measured at the filter outlet during this procedure must be belowthe limiting value.

In order to be able to comply with this limiting value at a volume ofthe fuel vapour filter which is still acceptable, it is necessary toremove the fuel vapour arising in shut-off phases of the internalcombustion engine again during the operating phases of the internalcombustion engine in order in this way, at the end of the test cycles,to achieve a loading condition of the fuel vapour filter in which thelatter is still capable of reliably absorbing the quantity of fuelvapour arising during refuelling. The quantity of flushing air requiredto remove a certain mass of fuel vapour in the regeneration of the fuelfilter increases exponentially with increasing unloading of the fuelvapour filter, i.e. as the degree of loading of the fuel vapour filterdecreases. This means that, given the relatively low loading conditionwhich the fuel vapour filter reaches during one shut-off phase of theinternal combustion engine within the test cycles, a very large quantityof flushing air is required in the subsequent operating phase of theinternal combustion engine in order to remove the fuel vapour from thefilter again.

Advantages of the invention

In contrast, the venting device according to the invention has anadvantage that, while a relatively small total filter volume isretained, the quantity of flushing air required for the regeneration ofthe fuel vapour filter in the operating phases of the internalcombustion engine is small. The subdivision of the filter into twofilter parts opens up the possibility of making the first filter partvery small, with the result that it achieves a very high degree ofloading in each shut-off phase of the internal combustion engine and canthus be unloaded again reliably and with certainty during the subsequentoperating phase of the internal combustion engine using only a smallquantity of flushing air. The dimensions of the second filter part arethen to be made sufficiently large to enable it, at the end of the testcycles concluding with a shut-off phase of the internal combustionengine--and hence with the first filter part fully laden--to absorb thevolume of fuel vapour arising during refuelling. The diffusion-hinderingconnection between the two filter parts ensures that fuel vapour doesnot already pass into the second filter part when the first filter partis not yet laden to the maximum extent, thus resulting in a premature,slight loading, of the second filter part, which cannot be removedbecause of the small quantity of flushing air during the individual testcycles. The flushing air is always sucked in via the outlet of thesecond filter part and flows through the two filter parts in the reversedirection to the fuel vapour and, laden with fuel, then passes via theintake system of the internal combustion engine into the combustionchamber of the latter.

Advantageous further developments and improvements of the venting deviceare possible by virtue of the measures presented hereinafter.

The volume of the first filter part is expediently to be adapted to theconditions of the stipulated test for testing the efficiency of theventing device, so that, in each test cycle, the first filter partachieves a very high, virtually maximum loading condition due to thequantity of fuel arising, which loading condition is reduced againcompletely with little flushing air in the subsequent test cycle beforethis loading condition is reached again, at the end of this subsequenttest cycle, in the shut-off phase of the internal combustion engine. Atthe end of the last test cycle, the first filter part is laden tosaturation. The volume of the second filter part is to be dimensionedsuch that--when the first filter part is completely saturated and henceno longer capable of absorption--it can bind the quantities ofevaporated fuel arising during the filling of the fuel tank under testconditions and achieves a large degree of saturation.

According to a preferred embodiment of the invention, the two filterparts are accommodated in separate containers, which are connected toone another in a manner which hinders diffusion. This has the advantagethat the very small first filter part can be arranged in the enginecompartment in order thus to be able easily to implement auxiliarymeasures for the regeneration or desorption of the fuel vapour filter,e.g. heating. However, the two filter parts can also be accommodated ina single container together with the diffusion-hindering connection.

The diffusion-hindering connection between the two filter parts can beconstructed in various ways. According to a preferred embodiment of theinvention, it is formed by a relatively long tube. However, it is alsopossible to produce this connection by means of a solenoid valve orvacuum-controlled valve which is opened during the operation of theinternal combustion engine and thus connects the two filter parts to oneanother. In the blocking condition of the solenoid valve during theshut-off phases of the internal combustion engine, the solenoid valveopens in the direction from the first to the second filter part above apressure which is below the filling pressure during refuelling of thefuel tank.

DRAWING

The invention is explained in greater detail in the description whichfollows, with reference to illustrative embodiments depicted in thedrawing, in which, the drawing is a each case in schematicrepresentation:

FIG. 1 shows a venting device connected to a fuel tank of an internalcombustion engine,

FIG. 2 shows a venting device according to a second illustrativeembodiment.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

In FIG. 1, 10 denotes a fuel tank which bears a fuel filler pipe 11 anda vent branch 12, which are arranged on its upper side. The ventingdevice for the fuel tank 10, said device being only schematicallysketched, has two containers 13, 14, each of which is filled withactivated carbon 15, 16. The containers 13, 14 filled with activatedcarbon 15, 16 form two filter parts 17, 18 of an activated carbon filterin which fuel evaporating in the fuel tank 10 can be bound. The twocontainers 13, 14 are connected to one another in series by a relativelylong tube 19 which prevents diffusion of fuel from the first filter part17 to the second filter part 18. The first container 13 is connected tothe vent branch 12 of the fuel tank 10 via a vent line 20. The vent line20 opens inside a hollow space 21 which is arranged centrally in thecontainer 13 and is formed within the activated carbon 15 by means of acylindrical screen 22. An inlet, end 23 and an outlet 24 are provided atopposite end faces of the container 13. While the tube 19 is connectedto the outlet 24 the inlet 23 is connected by means of an extractionline 29, via a flushing-air control 25, to the intake system 26 of theinternal combustion engine. The flushing-air control 25 serves for themetered admixture of fuel-laden flushing air to the fuel/air mixture ofthe internal combustion engine. An example of a flushing-air control isdescribed in DE 38 02 664 C1. Container 14, which is completely filledwith activated carbon 15, likewise has an inlet 27 and an outlet 28 atopposite end faces. The inlet 27 is connected to the tube 19 and theoutlet 28 is open to the atmosphere and serves for the entry of flushingair.

A so-called "on-board refuelling test" comprises three test cycles and asubsequent heating up of the tank by a defined amount. This procedure iscarried out three times in succession. At the end of the test, the tankis filled with a certain quantity of fuel. Each test cycle comprises anoperating phase of the internal combustion engine under predeterminedconditions and, following this, a one-hour shut-off phase of theinternal combustion engine. The volume of the activated carbon 15 in thecontainer 13 is dimensioned such that, at the end of each test cycle,the filter part 17 reaches a very high loading condition. In theoperating phase of the following operating cycle, the container 13 isfirst of all flushed with fresh air and the activated carbon 15 thusregenerated and is then loaded with fuel vapour again in the shut-offphase of the internal combustion engine. At the end of the third testcycle, i.e. after the heating up, the filter part 17 is laden with fuelvapour to just up to the degree of saturation. The tube 19 prevents fuelvapour from passing from container 13 to container 14 by diffusionduring these three test cycles. The volume of the activated carbon 16 incontainer 14 is dimensioned so that the fuel vapour arising during thefilling of the tank after the 3×3 test cycles, loads filter part 18 tojust up to the degree of saturation.

In each operating phase of the internal combustion engine, a suctionpressure is generated by the intake system 26, as a result of whichflushing air enters container 14 via the outlet 28, flows through theactivated carbon 16, the tube 19 and the activated carbon 15 incontainer 13 and finally, laden with fuel, passes in metered fashion,via the flushing-air control 25, into the intake system 26 of theinternal combustion engine. During this process, the activated carbon 15and 16 in the two containers 13, 14 is regenerated, with the result thatin subsequent shut-off phases of the internal combustion engine the fuelvapour filter comprising the filter part 17, 18 is capable of absorbingthe evaporating fuel, including the quantity of fuel vapour arisingduring refuelling, and thus of preventing escape into the atmosphere.

In the venting device represented schematically in FIG. 2, the twofilter parts 17, 18 are united in a single container 30. Thesmaller-volume first filter part 17 is spatially separated from thelarger-volume second filter part 18, the partition walls 31, 32 beingbuilt into the container 30 in such a way that a meander-shapedconnection is formed between the two filter parts 17, 18. In otherrespects, the construction and mode of operation of this venting deviceis identical to that described in FIG. 1.

The invention is not restricted to the illustrative embodimentsdescribed above. Thus, a large number of designs are possible for theconnection preventing fuel crossing over by diffusion from filter part17 to filter part 18. In FIG. 1, it is formed by a relatively long tube19 and, in FIG. 2, by a meander-shaped connection produced by means ofpartition walls 31, 32. However, it can also be effected by a solenoidvalve or vacuum-controlled valve which is always open whenever theinternal combustion engine is in its operating phase. In the shut-offphase of the internal combustion engine, the solenoid valve is closedbut is designed in such a way that, above a pressure slightly below thefilling pressure during the refueling of the fuel tank, it opens in thedirection from the first filter part 17 towards the second filter part18.

It is obvious that rising vapor goes from the fuel tank 10 to theactivated carbon filled tank 13 and after saturation the vapor goes vialine 19 to the activated carbon filled tank 14. During flushing, air isdrawn in via the outlet 28 of tank 14, passes through the activatedcarbon 16 in tank 14 and passes through line 19 to the tank 13. Theflushing air then passes through the activated carbon 15 and out via theend 23 to the flushing air control 25 and into the intake of the engine.

I claim:
 1. A venting device for a fuel tank of an internal combustionengine having a vent line which connects a vent branch of the fuel tank,via a fuel vapor filter having a storage effect for hydrocarbons, inparticular an activated carbon filter, to atmosphere, and having anextraction line which leads to the intake system of the internalcombustion engine and is connected to the fuel vapor filter, the fuelvapor filter is subdivided into a small-volume first filter part (17)and a large-volume second filter part (18) and the two filter parts (17,18) are connected to one another by a relatively long tube (19) whichprevents fuel crossing over as a result of diffusion and are arranged inseries in the flow of fuel vapor in such a way that the vent andextraction line (20, 29) are connected to the first filter part (17) andthe connection to the atmosphere is at the outlet (28) of the secondfilter part (18), and the volume of the first filter part (17) isdimensioned so that, after the completion of a test routine, comprisingtime phases of operation and of shut-off of the internal combustionengine, the first filter part (17) is laden to saturation with fuelvapor, and the volume of the second filter part (18) is dimensioned sothat the quantity of fuel which evaporates during the filling of thefuel tank (10) can be absorbed by the said second filter part with theachievement of a high degree of loading.
 2. A venting device for a fueltank of an internal combustion engine having a vent line which connectsa vent branch of the fuel tank, via a fuel vapor filter having a storageeffect for hydrocarbons, in particular an activated carbon filter, toatmosphere, and having an extraction line which leads to the intakesystem of the internal combustion engine and is connected to the fuelvapor filter, in which the fuel vapor filter is subdivided into asmall-volume first filter part (17) and a large-volume second filterpart (18) and the two filter parts (17, 18) are connected to one anothervia a diffusion-hindering means which prevents fuel crossing over aresult of diffusion and are arranged in series in the flow of fuel vaporin such a way that the vent and extraction line (20, 29) are connectedto the first filter part (17) and the connection to the atmosphere is atthe outlet (28) of the second filter part (18) and the connectionbetween said filter parts (17 and 18) of the diffusion hindering meansis effected by a solenoid valve which is open during the operation ofthe internal combustion engine and, in the blocking condition, opens atleast in the direction from the first filter part (17) to the secondfilter part (18) above a pressure below the filling pressure duringrefueling of the fuel tank (10), and the volume of the first filter part(17) is dimensioned so that, after the completion of a test routine,comprising time phases of operation and of shut-off of the internalcombustion engine, the first filter part (17) is laden to saturationwith fuel vapor, and the volume of the second filter part (18) isdimensioned so that the quantity of fuel which evaporates during thefilling of the fuel tank (10) can be absorbed by the said second filterpart with the achievement of a high degree of loading.
 3. A ventingdevice for a fuel tank of an internal combustion engine having a ventline which connects a vent branch of the fuel tank, via a fuel vaporfilter having a storage effect for hydrocarbons, in particular anactivated carbon filter, to atmosphere, and having an extraction linewhich leads to the intake system of the internal combustion engine andis connected to the fuel vapor filter, the fuel vapor filter issubdivided into a small-volume first filter part (17) and a large-volumesecond filter part (18) and the two filter parts (17, 18) are connectedto one another via a diffusion-hindering means which prevents fuelcrossing over as a result of diffusion and are arranged in series in theflow of fuel vapor in such a way that the vent and extraction line (20,29) are connected to the first filter part (17) and the connection tothe atmosphere is at the outlet (28) of the second filter part (18), andthe volume of the first filter part (17) is dimensioned so that, afterthe completion of a test routine, comprising time phases of operationand of shut-off of the internal combustion engine, the first filter part(17) is laden to saturation with fuel vapor, and the volume of thesecond filter part (18) is dimensioned so that the quantity of fuelwhich evaporates during the filling of the fuel tank (10) is absorbed bythe said second filter with the achievement of a high degree of loading.4. A device according to claim 2, characterized in that thediffusion-hindering connection of the two filter parts (17, 18) isproduced by a relatively long tube (19).
 5. A device according to claim2, characterized in that the diffusion-hindering connection is effectedby a solenoid valve which is open during the operation of the internalcombustion engine and, in the blocking condition, opens at least in thedirection from the first to the second filter part (17, 18) above apressure below the filling pressure during refuelling of the fuel tank(10).
 6. A device according to claim 3 in which said first filter part(17) is accommodated in a first container (13) said second filter partis accommodated in a second container (14), and the diffusion-hinderingmeans connection (19) is produced between said first and secondcontainers (13, 14).
 7. A device according to claim 4, in which saidfirst filter part (17, 18) is accommodated in a first container (13)said second filter part is accommodated in a second container 14, andthe diffusion-hindering means connection (19) is produced between saidfirst and second containers (13, 14).
 8. A device according to claim 5,in which said first filter part (17, 18) is accommodated in a firstcontainer (13) said second filter part is accommodated in a secondcontainer 14, and the diffusion-hindering means connection (19) isproduced between said first and second containers (13, 14).
 9. A deviceaccording to claim 1, in which said first filter part (17, 18) isaccommodated in a first container (13) said second filter part isaccommodated in a second container 14, and the diffusion-hindering meansconnection (19) is produced between said first and second containers(13, 14).
 10. A device according to claim 2, in which said first filterpart (17, 18) is accommodated in a first container (13) said secondfilter part is accommodated in a second container 14, and thediffusion-hindering means connection (19) is produced between said firstand second containers (13, 14).
 11. A device according to claim 3, inwhich the first and second filter parts (17, 18), and thediffusion-hindering means connection (31, 32) are accommodated in asingle container (30).
 12. A device according to claim 1, in which thefirst and second filter parts (17, 18), and the diffusion-hinderingmeans connection (31, 32) are accommodated in a single container (30).13. A device according to claim 2, in which the first and second filterparts (17, 18), and the diffusion-hindering means connection (31, 32)are accommodated in a single container (30).